This is a nationalization of PCT/GB99/04059, filed Dec. 6, 1999 and published in English.
The present invention relates to an industrial process to be used for nutrient removal, specifically for the removal of nitrogen and phosphorous, from water and wastewater. For example, it is applicable to industrial and municipal wastewater.
Conventionally, different processes for removing biological nutrients from water and wastewater have used a combination of activated suspended solids treatment or fixed film processes, as have been described in textbooks, professional journals and magazines. Known processes disclose the removal of nitrogen of phosphorous, but not the removal of nitrogen and phosphorous together.
In biological nitrogen removal, the incoming domestic crude sewage contains nitrogen in the form of industrial ammonia, urea and fertilizer. During the process, nitrogen is first converted to nitrites by bacteria, for example, by species of Nitrosomonas, in the presence of oxygen, and then into nitrates by bacteria, for example, by species of Nitrobacter. In order to de-nitrify, that is to remove nitrogen from the solution, nitrates need to be fed into an anoxic tank where the oxygen level is less than 0.5 mg/l. De-nitrifying bacteria, for example, of the species of Pseudomonas, Achromobacter and Bacillius, reduce the nitrates to nitrogen gas using organic carbon for metabolism.
In all known cases the biological removal (i.e. relying on naturally occurring bacteria for treatment) of nitrogen involves building tanks referred to as anoxic tanks, which are partially devoid of oxygen, and re-circulating a proportion of nitrified effluent into them. Under anoxic conditions with a carbon source, naturally occurring bacteria will de-nitrify the nitrified effluent, which leads to the production of nitrogen gas.
Phosphorous is present in domestic sewage due to the influence of detergents, fertilizers and industrial effluents. Biological phosphorous removal requires three distinct phases. 1. An anoxic phase during which a proportion of the incoming poly-phosphorous is taken up by phosphorous accumulating bacteria. 2. An anaerobic phase (completely devoid of oxygen) during which the poly-phosphorous is regurgitated into solution by the bacteria and during which volatile fatty acids produced by decaying organic matter in solution are taken up by the bacteria in the form of poly-beta- hexabutyrate, which increases the digestion capacity of the bacteria for the third phase, 3. An oxic phase, for example, in an aeration tank, during which phosphorous accumulating bacteria will take up the regurgitated phosphorous in solution plus any other available form of phosphorous in solution in the form of ortho-phosphate.
The most popular of the known technologies for removing nitrogen from wastewater is referred to as xe2x80x98the BARDENPHO processxe2x80x99. This process essentially alternates an aerobic zone with an anoxic zone in different tanks to achieve nitrogen removal.
It is an object of the present invention to provide a process for removing both nitrogen and phosphorous from wastewater in a single process.
It is a second object of the present invention to provide a process for the treatment of wastewater for the removal of nitrogen and phosphorous having a reduced number of steps and being both cost effective and more efficient.
It is a further object of the present invention to provide a process wherein recycling of a mixed liquor during the process leads to a greater degree of de-nitrification, while also removing a greater proportion of organic carbon from the effluent.
According to the present invention there is provided a process for the removal of at least one of wastewater or raw sewage, including biological removal of nitrogen and optionally phosphorous therefrom, said process comprising at least a first step, in a tank or compartment which is sized and/or converted to be suitable for both anoxic and anaerobic conditions, involving feeding the wastewater/raw sewage into the tank or compartment so as to partially fill the tank or compartment and so as to provide anoxic and anaerobic regions within the wastewater/raw sewage and an oxic region within the tank or compartment.
Preferably, the first step comprises feeding the wastewater/raw sewage into a balancing tank or a converted primary settlement tank. The first step may comprise feeding the wastewater/raw sewage into a balancing tank and a primary settlement tank.
The process preferably further comprises a second step comprising processing in an aeration tank suitable for aerobic conditions and a third step, acting as a clarifier, involving recycling a proportion of mixed liquor from the second step back into the first step.
Preferably, a proportion of the sludge and associated micro-organisms retrieved from the third step are recycled back into the second step to maintain a viable population of micro-organisms. A proportion of sludge and mixed liquor may also be recycled from the third step back into the first step.
Also preferably, an external carbon source may be introduced to the first step.